The present disclosure relates generally to chemical insect attractants. In particular, chemical insect attractants effective to attract the Asian citrus psyllid, known as D. citri, are described.
The Asian citrus psyllid, Diaphorina citri (D. citri), vectors three phloem-restricted bacteria in the genus Candidatus Liberibacter, which have been associated with huanglongbing (HLB), otherwise known as citrus greening disease. Citrus trees infected by HLB produce small, misshapen fruit characterized by bitter taste, rendering the juice and related products unmarketable. Infected trees gradually decline, drop much of their fruit load and ultimately die.
D. citri was first reported in Florida in 1998, but has invaded many more regions, which include all citrus growing areas of the continental U.S., Puerto Rico and Hawaii. HLB was first discovered in Florida in 2005 and is now well-established. It has been confirmed in several commercial groves in Texas and in only one residential tree in California. Whereas the psyllid has been detected in several areas in Arizona, neither psyllids nor plant material has tested positive for Liberibacter. 
Current sampling protocols for adult D. citri rely on passive sticky traps, which capture D. citri by incidental or random encounters of flying adults with these sticky surfaces or by tap sampling in which tree branches are shaken to dislodge psyllids onto a sticky surface held below the branch. This renders adult psyllid monitoring for forecasting or evaluating insecticide applications inaccurate.
Currently, a semiochemical-based lure (chemical used for communication between individuals) to attract D. citri is not commercially available. D. citri exhibits strong preference for citrus volatiles and aggregate and lays eggs exclusively on young unexpanded leaves. Thus, plant-related chemicals are crucial signals used by adults for plant selection. In addition, there is evidence documenting that mate location in D. citri is mediated by a volatile sex pheromone and hydrocarbons emitted from the cuticle or outer surface of the insect.
Thus, there exists a need for D. citri chemical attractants that improve upon and advance the state of the art. Examples of new and useful chemical insect attractants relevant to the needs existing in the field are discussed below.
An insect attractant may comprise a blend of volatile organic compounds. The blend of volatile organic compounds may comprise alpha-phellandrene, beta-caryophyllene, and at least one additional volatile organic compound. In one embodiment, the ratio of alpha-phellandrene to beta-caryophyllene in the blend may be 1:0.5 to 1:2. In one embodiment, the blend of volatile organic compounds may comprise 15 to 60 wt. % alpha-phellandrene and 10 to 50 wt. % beta-caryophyllene. In one embodiment, the at least one additional volatile organic compound may be selected from the group consisting of: beta-phellandrene, gamma-terpinene, ocimene, and terpineol.